The US–UK treaty's Article 18 gives UK pensions cross-border recognition, so a workplace pension or SIPP is generally not treated as a taxable foreign trust. But the treaty does not align the systems: employer contributions, growth and especially the 25% tax-free lump sum are treated differently, and the pension is still reportable on FBAR and usually Form 8938.
This is the area where confident wrong answers are most common, on both sides of the Atlantic. British advisers describe the 25% lump sum as tax free because in Britain it is. American preparers with no cross-border practice treat a SIPP as a foreign grantor trust because it looks like one.
Both errors are expensive, and the correct position is genuinely less certain than either camp admits.
Article 18 provides that pensions arising in one state and beneficially owned by a resident of the other are generally taxable only in the state of residence, and it gives reciprocal recognition to pension schemes so that they are not treated as ordinary foreign trusts.
That recognition is the valuable part. Without it, a SIPP would face the foreign trust regime with Forms 3520 and 3520-A and their punitive penalties. With it, most US practitioners take the position that those forms are not required.
What Article 18 does not do is make UK pension outcomes tax free in America. It allocates and recognises; it does not exempt.
| Question | UK treatment | Typical US position |
|---|---|---|
| Employer contributions | Not taxable on the employee | Generally not currently taxable under Article 18(5) |
| Employee contributions | Relief at marginal rate | Deduction is limited and often unavailable in practice |
| Growth inside the fund | Tax free | Generally deferred under the treaty rather than taxed annually |
| 25% lump sum | Entirely tax free | Frequently taxable — the treaty does not clearly exempt it |
| Ongoing pension income | Taxable as income | Taxable in the state of residence |
The lump sum is the one that hurts. Drawing 25% of a large pot the year you become US resident, or while remaining a US citizen in Britain, can convert a tax-free British benefit into a fully taxable American receipt.
The mirror problem is just as common. A 401(k) or IRA held by someone who moves to Britain remains a US-recognised pension, and Article 18 works in both directions — but the timing of withdrawals, the interaction with UK tax on the arising basis, and the treatment of Roth accounts all need planning before the first distribution.
Roth accounts are the sharpest case. A Roth IRA is tax free in America by design, and obtaining matching UK treatment depends on the account qualifying as a pension scheme for treaty purposes.
Almost every good outcome here depends on sequencing. Which country you are resident in when you take the lump sum, whether you crystallise before or after a move, and how a transfer between schemes is characterised are decisions with very different results and no ability to unwind afterwards.
That is why we would rather see a pension question two years early than two weeks late.
The pension itself is recognised under Article 18 of the treaty and is generally not treated as a taxable foreign trust, so growth is typically deferred rather than taxed annually. Distributions are taxable in the state of residence. The contentious part is the 25% lump sum, which is tax free in Britain but frequently taxable in America.
Very possibly. The treaty does not clearly exempt the pension commencement lump sum from US tax, and the conservative and common position is that it is taxable on a US return even though Britain charges nothing. Because the amounts are large and the decision is irreversible, take advice on sequencing before drawing it.
In most cases yes. A UK workplace pension or SIPP is generally a foreign financial account for FBAR purposes and counts toward the $10,000 aggregate threshold, including small auto-enrolment pots people forget. Treaty recognition affects how the pension is taxed, not whether it is reported.
Generally not, where Article 18 recognition applies — that recognition is the main reason a SIPP is not treated as an ordinary foreign grantor trust. It remains a position rather than an absolute certainty, so it should be taken deliberately and consistently rather than assumed.
Generally not, which is one of the strongest arguments for holding funds inside a recognised pension rather than in an ISA or a general investment account. The same fund held outside a pension wrapper is normally a passive foreign investment company requiring Form 8621 and taxed under the punitive excess distribution regime.
It remains a recognised pension and Article 18 operates in both directions, so distributions are generally taxable in your country of residence. The planning issues are timing, the interaction with UK taxation on the arising basis, and Roth accounts, where matching UK treatment depends on the account qualifying as a pension scheme for treaty purposes.
The sequencing decision cannot be unwound. We model the UK and US positions together, well before you draw.
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